Temperature Inversions

In a previous working life I was a weather observer, but we dealt only with surface conditions. I imagine that the inversions that exist in mid-winter in interior Alaska would be similar to what I could expect here in the Canadian arctic, though we do have more wind on the coast which probably tends to mix up the air unless we get several days of calm conditions, and that's not very common.

I know that several on here live or have worked in central Alaska. What have you experienced with regard to winter temperature inversions? What's the biggest temperature difference between the surface and flight altitude you've seen? At what altitude do/did you find the warmest air?

All this just to satisfy my curiosity, and maybe make my flights a little more comfortable. ;-)

Larry - Maybe do some reading regarding Skew-T charts. Might be helpful - maybe??? You have the background to understand that stuff, but I don't.

Hi Larry. The info is available on a larger scale via the RAOB upper air sounding Skew-T Log-P charts. It's not uncommon to see a +20 to 40F rise within 1000' of the surface with the upward trend starting around 5-700'/ AGL near Fairbanks. Convert to Metric as needed. And yes winds above the inversion can be brisk yet fail to scour out the deep cold especially in low spots known for cold intrusion and shielded by surrounding terrain. The degree of cloud cover moderates IR radiation and surface cooling. Any thin to broken layer above can retain warmth below if the wind doesn't mix the atmosphere.

It can be issue flying from cold surface air to warmer moist air close above as the cold airframe will condense any available moisture and that's instant thin rime ice and reduced visibility through the windshield. The reverse can be true when descending but then the condensation happens inside the cockpit windows as moist air condenses.

Chart explanation: https://www.weather.gov/jetstream/skewt and https://www.spc.noaa.gov/exper/soundings/help/index.html
Alaska soundings via menu: https://www.weather.gov/afc/upperAir
Canadian soundings via menu: http://meteocentre.com/numerical-we...knife&mod=gemreg&run=18&lang=en&map=ca&hh=000

A fun explanation of inversion by Rick Thoman NWS for Fairbanks: http://fnsb.us/transportation/AQCon...nter Making Sense of That Crazy Inversion.pdf

Gary

If you observe departing piston aircraft exhaust during their climb through an inversion to warmer air the visible exhaust moisture in the cold layer can quickly reduce or disappear above the inverted layer. Also in calm air visible furnace exhaust will rise then turn sideways near the top of the cold layer.

Gary

We had a little inversion last Sunday night



Glenn

As kids in Upper Michigan we used to call them free popsicles. Break them off and enjoy. Lake effect freezing precipitation did it. Don't chew the sticks.

Gary

BC12D-4-85 said:

If you observe departing piston aircraft exhaust during their climb through an inversion to warmer air the visible exhaust moisture in the cold layer can quickly reduce or disappear above the inverted layer. Also in calm air visible furnace exhaust will rise then turn sideways near the top of the cold layer.

Gary

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Yes, I have noticed that, Gary. I just didn't make the connection because I always thought the inversion layer would be much higher, but it seems to sometimes be as low as a couple of hundred feet.

We rarely get freezing rain here, probably because it's usually just too cold both above and below the boundary.

Larry

Back in the 1960's there were few dwelling in the hills surrounding Fairbanks. Rough trails and few subdivision roads with electric power discouraged occupancy...unless you had something the hide from the authorities. Eventually land became available and the rush to climb above the winter inversion was on especially if you knew the local weather forecasters or pilots who were aware of the marked temp changes with altitude.

We still live in the swamps but someday I keep saying I'll escape the winter air pollution that's a product of trapped air and combustion. We have the #1 worst winter air quality in the nation: https://dec.alaska.gov/air/anpms/communities/fbks-pm2-5-curtail-alert/

Gary

A few months from now I'll try to post a picture of our springtime inversions that produce a very strong mirage effect over the sea ice. The air close to the ice is chilled and warmer air moves in on top. It's quite dramatic but produced by a somewhat different mechanism than mid-winter inversions (I think!). The boundary in that case seems to be at about the 100-foot level.

That same sharp boundary can also result in a phenomena called tropospheric ducting. VHF radio signals can travel much longer-than-normal distances between the surface ice and the inversion boundary. It's uncommon, but I've heard a low-powered FM radio signal from a station in Cambridge Bay, 240-miles to the east. The path is almost totally over sea ice, and that 20-watt FM signal would normally only be heard for about 10-miles.

Larry we get that mirage effect as well mainly to the south over smooth terrain: https://weather.com/news/weather/news/2018-01-17-fata-morgana-fairbanks-alaska

And the VHF ducting in winter. At my lake cabin it was common to enjoy winter ham radio VHF over a similar distance but sea and ice have even lower ground loss. I could get TV from Anchorage (~220 miles SE ) via knife edge and reflective bending before they went to digital mode propagation.

Gary

Fata Morgana

The picture is from Tin City, near Wales, on the Seward Penninsula. King Island is about 40 miles away and appears to be surrounded by several thousand foot tall vertical cliffs. The inversion that day was more than 30 degrees warmer, as you climbed a thousand feet. I have seen mirage or Fata Morgana in the flats South of Fairbanks make the 10,000 foot mountains by Healy look much taller than the 20,308 foot Mount Mckinley.

Gordon Misch said:

Larry - Maybe do some reading regarding Skew-T charts. Might be helpful - maybe??? You have the background to understand that stuff, but I don't.

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I’ll save every body else the time to “google it” (I sure had to).

For twenty years, I lived six miles or so northeast of Fairbanks, overlooking the Tanana Valley. I worked in town, and when it was really cold in Fairbanks, as in colder than -40, it would be around -20 at our home, which was maybe a couple hundred feet higher than the city.

The weirdest weather phenomena I think I ever ran into involved a hard inversion. I flew a Cessna 185 on skis north from Fairbanks to the Yukon Flats, about 100 miles north. At the time, the only reporting point on the Flats was Fort Yukon, and on this particular day, FYU was reporting -19 F and a light breeze. FYU is just over 400 msl, FAI is 434 msl, and the White Mountains lie between.

I had been trying to get to a site southwest of FYU for several days, but it had been really cold. So, the relatively warm temp of FYU this day was encouraging. Fairbanks, however, was a solid -30 F. That seemed weird to me, since the Fort is generally colder than FAI in winter and hotter in summer. But, anyway....

So, cleared the White Mountains, and descended toward the lake I was headed for. FYU AWOS was still reporting -19 F. My OAT instrument verified about -20 F.

I swung around to land on the lake, which sat in a bit of a depression, and was surrounded by trees. As I descended below the trees, it felt like I was diving into water, and it was astounding how quickly the cockpit cooled off.

I landed, taxied back to the shore, and when I got out of the plane, it was obviously REALLY cold. There was an "official" weather station there, and the thermometer on it read -58 F.

I quickly jumped back in the plane, and departed, using limited throttle. As I came up out of the lake, to about 100 feet agl, the temperature was again about -20.

I never saw such a hard, shallow inversion before or since. The key was that there was a gentle breeze of ~ 6 knots or so, which was mixing the atmosphere above the trees, but that sump and the trees surrounding it were protected.

When I first moved to FAI, I picked up a brand new Cessna 185. That airplane came with the official Cessna "Cold Weather Kit", consisting of two plates with small, rectangular inlets that blocked off the cowling air inlets, and an induction intake plate with a ~ two inch diameter hole in it.

So, first winter, when it got cold, as in -20 or so, I dutifully installed that kit, and off I went. Problem was, if I climbed above 500 or 1000 feet, the engine would start to overheat, because the air at those heights was warmer. But, of course, where I was going was north and colder. The conundrum was to leave the plates in place and stay way low, down in the very cold air (dumb idea) or remove the kit.

I removed the plates on the main air inlets and put some duct tape over the oil cooler, left the induction plate in place and flew that plane for a number of years in very cold temperatures.

MTV

Thanks Mike. I knew I could count on you for a story about inversions!

Another interesting phenomenon can happen when flying out of or into a deep cold inversion...instant ice fog along the flight path. The engine exhaust provides ice crystal nuclei to start the reaction and the plane's vortex wake mixes the nearly saturated air (temp/dew points close). I've flown over small lakes located in a cold inversion hole to check the snow conditions only to have them go IFR behind me. It takes 30-40 below or colder to make that happen.

Gary

Thanks everyone for your input. As an old weather observer/FSS/ham radio guy I find it very interesting.

I've never been to Alaska, though it's on my bucket list. Fairbanks and many places along the Yukon/Alaska border get some seriously cold temperatures. We are a little farther north than Fairbanks, but on the coast so the temperatures rarely get lower than -40. I've seen -49F only once in my 50 years here.

The killer here is the wind chill.

Question Larry....what do local folks do if stuck in a whiteout blow? Do they carry shelter or build something? It must happen often enough for them to have figured out a plan.

Gary

Gary - I've noticed that, over the years, fewer men go out hunting in the winter. The declining caribou herds may have something to do with that, but modern life, even in these small settlements, is pretty comfy nowadays. People seem content to stay at home (especially during the cold months), watch TV, smoke the (now legal) Canadian reefer and visit the welfare office every two weeks!.

Since I retired, I spend the winter making as much coin as possible at my part-time job so that I can take off to my cabin in March and April (skis) and August/September (floats).

No smart person travels without a good tent. There's no wood here so the only way to heat a tent is with a Coleman stove (and hope you don't run out of fuel). The people who knew how to quickly build a snow house have long gone to the happy hunting ground. Weather forecasts are much better than they used to be, and many hunters carry a GPS, Spot, HF radio or sat 'phone now. Snowmobiles have better range and are more reliable (but more costly to buy). Back in the days of the 15 hp, 2-stroke, single cylinder Ski-Doo I used to carry a spare engine on the komatik and could change it out in 20-minutes. Even if a guy could afford to keep a spare engine for a modern sled, it would be a major job to swap it out in the field, what with the liquid cooling, fuel injection and all.

I'm afraid my days of sleeping in a tent at -40 are over. I don't miss it!

Thanks Larry for the report. No or poor hunting/trapping opportunities would limit travel unless there was a camp up the Coppermine River to go to. I carried a three sided teepee tent/windbreak made of canvas and supported with extendable metal tent poles. Had a sod flap to pile snow on at the base and a zipper plus tied flap. Cold to indoors in 5 minutes plus camp stove heater. Good place to make tea and fix the sled. But I'm sure the early Inuit settlers had it also figured out and made stone or snow shelters if not hides over the brush bows they always carried.

I braved -30F today walking the dog to and from my idling car at the airport for 45 minutes and considered myself quite the adventurer.

Gary

35 degrees at my place this AM, 15 miles and 1200' higher then in town, and the wind blowing 25-30+mph. The town's airport weather station was reporting 9 degrees, and dead calm. I had a very large truss setting (60'span, bonus room type) crane job to do, so waited for the contractor to confirm it was calm at the job site, then headed in. Sure, enough dead calm, and now up to 20 degrees, we got a lot done and then right after a lunch break it went from near calm to 20+ mph within 5 minutes, and we bagged it for the day. It's good to have a crane op who flies a light plane, as I had warned him that the wind WOULD come up at some point, and it'd be sudden, so brace good as you go!

I don't know the meteorological explanation, but when it's windy at my elevation in the morning, but calm down in the valley, I can reliably predict it will get windy in the valley as the day proceeds. Something to do with the barometric pressure I'm sure.... then there are the days when I launch in calm winds, get up and find I have big winds aloft, then land at my place and it's calm again. Then an hour or two later, bang, it's windy at my elevation, but still calm in the valley.

Any solar heating can start ground level convection then mixing above. Also depends on degree of reflective snow cover (albedo). At 64* North with snow that's not possible for another 4-6 weeks. In Idaho your sun is about 26* above the horizon on January 21st while ours is 5.5*. I takes 12 hrs of daylight and a 26* sun angle on March 21 here to start melting the frozen dog poo.

Gary

BC12D-4-85 said:

I've flown over small lakes located in a cold inversion hole to check the snow conditions only to have them go IFR behind me. It takes 30-40 below or colder to make that happen.

Gary

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I've had that happen when running on the step along the length of a lake, then when pulling up looking behind finding the pond completely socked in. Temperature was well above freezing. Then repeated the phenomenon on the adjacent lake.

Skiers are well aware of inversions. Warmer at the top. Common. The coolest feature of inversions around south central Alaska is how it makes sunsets over the Alaska Range look like the mountains are square with notches, like the top of a castle. Or sometimes the mountain scene is reflected in the sky. Fun to see except it means its colder than a witch’s tit outside.

skywagon8a said:

I've had that happen when running on the step along the length of a lake, then when pulling up looking behind finding the pond completely socked in. Temperature was well above freezing. Then repeated the phenomenon on the adjacent lake.

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I've not seen that on floats yet but maybe temp/dewpoint close and cool stationary air next to lake with warmer moist air above mixed by plane? Here in winter the airport snowblowers can create fog - first they blow snow and then if no wind and the right condx like low sun angle and an inversion fog forms over the ground. Makes me wonder if CAT II or III ops makes it worse for the next plane?

Gary

Edit: Advection fog with he plane doing the mixing?

Gary, It was too long ago to remember any details. It was on an high overcast zero wind day. Could have been late in the day when the dew point was just right. It was an experience to remember.

Lots of ice for the mixed drinks in Alaska this week. Hit run and watch the fun: https://www.tropicaltidbits.com/ana...ns&region=ak&pkg=T2m&runtime=2020010506&fh=-6

Gary

One really cold winter's day in Fairbanks, I drove down to our hangar at the airport to verify that heat was on, and everything was working okay. Temperature was in the serious business range, I think it was -55 or so.

This was on a weekend, the the temperature had just dropped out the bottom, so no ice fog in the valley....yet.

I arrived at the airport, checked on the hangar, and everything was fine. As I was walking back to my car, I heard a helicopter.

The helicopter manufacturer Agusta (from Italy) was cold weather testing a new, very large helicopter in Fairbanks that winter, and the helicopter I heard was this huge beast, inbound to FAI. They'd been out in the valley, taking advantage of the very cold temps there in this 40 + passenger helicopter, and now they were inbound to the ERA Helicopter hangar next to our hangar, that they'd leased for the winter.

As always, I paused to watch the approach and landing. They came in at fair speed, pretty much right over where I was parked on the ramp, and made a very smooth and quick landing......the reason being that their wake was turning EVERYthing behind that helicopter to solid fog.

This was right at sunset, around 2:30 or 3:00, and the sight was absolutely spectacular from my vantage point.....this huge helicopter, slowing and dragging solid vortices of ice fog behind them as they descended and landed. It's hard to describe, but withing seconds of the touchdown, the entire airport area was solid IMC. A short time later, I checked the ATIS and they were reporting less than 1/8 mile in fog, RVR 100.

There were no other airplanes in the immediate area at the time, and obviously, conditions were just perfect for this phenomena. I had done something similar a few times, making low passes to lakes on skis, but I'd never seen such a large area affected.

One of those things you really wished you'd had a video of.

A few days later, I ran into one of the Italian pilots who'd been flying that day. He'd flown with me some on skis for grins. I told him I was right there when they landed, and asked him if he was aware of the fog triggering behind him. One of the engineers in the back informed the pilots of the fog developing, and he planted the thing, with no hover to landing. He too was amazed that the entire airport went IMC instantly.

MTV

It sounds like Fairbanks has some very interesting weather. I'll have to see it for myself one day.

I would also like to see all the airplanes over there. I'm a little bit tired of having the only privately-owned, non-commercial 'plane in all of Nunavut - an area of 725,000 square miles! Nobody to fly with!

Hey Larry are there any UAV's over there yet? They are getting quite popular and appear to be a great way to look over the country and find that Grizz headed towards your camp.

CA's laws: https://www.tc.gc.ca/en/services/aviation/drone-safety/flying-drone-safely-legally.html

Gary

BC12D-4-85 said:

Hey Larry are there any UAV's over there yet? They are getting quite popular and appear to be a great way to look over the country and find that Grizz headed towards your camp.

CA's laws: https://www.tc.gc.ca/en/services/aviation/drone-safety/flying-drone-safely-legally.html

Gary

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There's a few of them here. I've had one myself for a couple of years. Seemed like a good idea at the time, but I have too many toys, too many jobs and too many wives (one). Maybe one day I'll get a chance to play with it ....uh, the drone that is!